I read the SCJP Sun Certified Programmer for Java 6 Study Guide book and bought the SCJP Sun Certified Programmer for Java 6 Practice Exams book.
Both books helped me tremendously and were really great!
Thank you Kathy Sierra, Bert Bates and all other people who helped writing them!
Oracle Java SE6 Certified Programmer
Oracle Java EE5 Certified Web Component Developer
Pivotal Certified Spring Professional
Certified ScrumMaster